Electrical switches typically operate to open and close an electrical circuit by moving one or more contacts between contact positions. A switch that is used to control one circuit is known as a single pole switch. In many instances, two or more switches are to simultaneously energize or de-energize two or more devices. For such instances, a multi-pole switch arrangement may be used. Depending on the application, the difference in the timing between the on/off times of the switch poles (i.e., the “simultaneity”) can be important and may be regulated as maximum specified values through various industry, agency or military standards. Many times, the specified simultaneity can be relatively difficult to achieve. This can be especially true when precision switches are needed with very precise and repeatable on/off positions and/or small differential travels (which is the difference in the on and off position). Low simultaneity in switch applications can be further complicated by slow switch actuation speeds.
Presently, multi-pole switch simultaneity is accomplished via three different techniques. One technique involves single, multi-pole switch designs having a single operating plunger and utilizing complex mechanisms to achieve simultaneity. However, these switches tend to be relatively large, which limits their potential usefulness. Furthermore, the mechanism complexity limits the level of precision that can be achieved in terms of on/off position repeatability and low differential travel.
A second technique that is used is ganging together two or more separate precision snap-action switches, each with their own operating plunger. A separate mechanism is provided to operate all the switches. The difficulty with this technique is that the individual switches must first be sorted to attain substantially identical on/off positions. This sorting operation can be relatively time-consuming and costly. Moreover, even with doing so, the level of simultaneity that can be achieved for both the on position and the off position remains limited because each individual switch has slightly different differential travels.
A third technique is similar to the second, in that two separate switches with a separate actuating mechanism are used. However, with this third technique, a single actuating mechanism is fitted with adjustment features, such as bendable tabs or adjustment screws. This can be relatively costly and, like the second technique, the level of simultaneity that can be achieved for both the on position and the off position remains limited.
Other potential concerns with presently known electrical switches include reliable control of low electrical loads and resistance to shock and vibration. Reliable control of low electrical loads implies that low electrical resistance is maintained when the switch is in the on position. The electrical resistance is largely a function of the contact force, which is the amount of force that is holding the switch contacts together. The higher and more stable the contact force, the lower and more stable the electrical resistance. Exposure to shock and vibration can cause the switch contacts to separate, resulting in unintended interruption of the electrical current flow. Good resistance to vibration and shock requires that the switch contacts remain in electrical contact. The higher and more stable the contact force, the better the shock and vibration resistance.
Hence there is a need for a single, relatively small-size, multi-pole switch with a single operating plunger and low differential travel that also has a relatively small simultaneity characteristic. There is also a need for a switch with higher and/or maintained contact forces during switch operation when the switch is in the on position and when the switch is exposed to shock or vibration. The present invention addresses at least these needs.